Ethylene glycol (EG) is an important organic chemical raw material, which is mainly used for producing polyester fibers, antifreezes, unsaturated polyester resins, lubricants, plasticizers, non-ionic surfactants and explosives. In addition, ethylene glycol can also be used in such fields as coating, photographic developer, brake fluid and ink, as the solvent and medium of ammonium perborate and for producing special solvents like glycol ether. Ethylene glycol has a wide range of uses.
At present, China has surpassed the U.S. and become the largest ethylene glycol consumer in the world, an average annual growth rate of the domestic apparent consumption from 2001 to 2006 is 17.4%. Although the production capacity and production of ethylene glycol in China increase rapidly, due to the vigorous development of industries like polyester, they still cannot meet the growing market demand, which requires imports in large quantities every year. Moreover, the imports show growth year after year.
Currently, both domestic and foreign large industrial productions of ethylene glycol adopt the process route of direct hydration of ethylene oxide, namely pressure hydration. The production technology is basically monopolized by three companies including Royal Dutch Shell, U.S. Halcon-SD and the U.S. UCC. In addition, the research and development work of the new synthesis technology of ethylene glycol has been making progress, for example, companies such as Shell, UCC, Mendeleyev University of Chemical Technology of Russia, Shanghai Research Institute of Petrochemical Technology, etc. have successively developed a technology for producing ethylene glycol by the catalytic hydration of ethylene oxide; Halcon-SD, UCC, Dow Chemical, NsKK and MCC have successively developed a technology for producing ethylene glycol by the ethylene carbonate process; Dow Chemical and other companies have developed a technology for producing ethylene glycol by the co-production of EG and dimethyl carbonate (DMC).
As to the direct hydration, it produces the reaction products of high water content, has a long process of the subsequent devices (evaporator), huge equipment and high energy consumption, and has an overall yield of the process of only 70%, directly affects the production cost of EG. Compared with the direct hydration process, the catalytic hydration process significantly reduces the water ratio and meanwhile obtains relatively high EC conversion ratio and ethylene glycol selectivity. If the problems of the catalyst stability and the relevant engineering technical problems are solved well, it will be the trend to prepare EG by the EC catalytic hydration process instead of non-catalytic hydration process. The technology of producing ethylene glycol by the ethylene carbonate (EC) process, which has relatively large advantages over the direct hydration of EO in terms of the EC conversion ratio, the ethylene glycol selectivity, the consumption of the raw materials and energy, is a leading process. The co-production technology of ethylene glycol and DMC can make full use of the CO2 resources by-produced by ethylene oxidation. In the existing EC manufacturing devices, only the addition of the reaction step for producing EC can produce two very valuable products. Said technology is very attractive.
However, the common drawback of the above processs is they need to consume ethylene resources. Under the current situation where ethylene is mainly obtained by conventionally refining the oil resources, and the global oil prices will be at a high level in the next period of time, producing ethylene glycol by using natural gas or coal that is abundant and cheap instead of oil (non-oil route, also referred to as CO route) has advantages of being able to compete with the conventional ethylene route. Among them, the new technology of synthesizing EG by synthesis gas may exert significant impact on the innovation of the EG production process. It is a very attractive coal chemical industry route to prepare dimethyl oxalate with carbon monoxide as the raw material and then prepare ethylene glycol by hydrogenating dimethyl oxalate. Nowadays, both domestic and foreign studies in preparing dimethyl oxalate with carbon monoxide as the raw material have achieved excellent effects, and the industrial production has been mature. However, as regards the preparation of ethylene glycol by the hydrogenation of dimethyl oxalate, there is still much research work to be required, especially, there is no good breakthrough regarding how to effectively improve the selectively for ethylene glycol and enhance the stability of the catalyst.
Document CN101138725A discloses a catalyst for synthesizing ethylene glycol by the hydrogenation of the oxalic ester and a process for preparing the same, the catalyst uses the copper metal as the active component, and zinc as the promoter, and is manufactured with the coprecipitation process. However, said catalyst leads to low conversion ratio of oxalic ester. Meanwhile, there is no report on the stability of the catalyst.
Document “Petrochemical Technology”, 2007, vol. 36, No. 4, p340˜343 describes a study on the reaction of synthesizing ethylene glycol by hydrogenation of dimethyl oxalate using Cu/SiO2. However, said catalyst has poor selectivity, and there is no report on the stability of the catalyst.